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LM48580: Driving a piezo from two sources

Christian Greeff
Prodigy 570 points
Part Number: LM48580
Other Parts Discussed in Thread: LM48560

Greetings,

I have an application where I need to drive a piezo from two sources:

-Normal operation where input is driven by standard audio source.

-Secondary backup operation where a GPIO pin can turn on/off the buzzer by triggering at FET.

I think the circuit below should allow for proper operation, however I wanted to verify this.

There is a current shunt (likely ~10mohm) in series with the speaker output for current feedback.

I also added a shotkey diode to prevent any reverse current flow in the condition where the the LM48580 is unpowered, and the pizeo is running in backup mode. 

Feedback on this would be greatly apprecitated.

Best Regards,

Christian Greeff

  • 0
    TI__Guru** 102045 points

    Hi Christian,

    You should make sure to pull SDHN pin low when enabling the FET control, or perhaps LM48580 or completely powered down?
    Not related to LM48580 functionality, but how is the FET going to drive the piezo? Is it going to be switching like a PWM? Or simply driving 5V DC to it? Just want to make sure LM48580 is compatible with how the piezo is driven.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    TI__Prodigy 570 points

    Hi Ivan,

    Thanks for your reply.

    That is good feedback to pull SHDN pin low when enabling the FET control. I assume it would still be a good idea to keep the shotkey diode, correct?

    The piezo is likely just going to be switched by the FET on or off with 5V DC. Would PWM control be an issue?

    Best Regards,

    -Christian

  • +1 in reply to Christian Greeff
    TI__Guru** 102045 points

    Hi Christian,

    Yes, keeping the diode is still good idea.

    PWM using the FET may be OK, my concern was that if the piezo has to be driven with DC voltage only, that is not what LM48560 does. What LM48560 is intended for is to drive the same signal it receives at the IN+/IN- terminals, not a DC voltage. But if that is not a concern then it should be OK.

    Best regards,
    -Ivan Salazar
    Applications Engineer